Fiber optic cables have been commonly deployed by installing them in ducts by blowing or pulling, burying them in the ground, or suspending them between above-ground poles. Traditional duct installation, however, uses space inefficiently. Typically, one cable per inner duct has been the maximum capacity although in some cases two cables have been pulled-in or jetted-in.
Recently developed optical microcabling technology has been introduced for the deployment of fiber optic cables to increase use of the conduit space and to enhance profitability of the current (and/or future) telecommunications infrastructure. This technology involves the use of standard inner ducts in which microducts are jetted, followed by the jetting of microduct cables or microcables into the microducts when required. Although originally intended for business access networks (FTTB) and fiber-to-the-home (FTTH), this technology has been used successfully in long-haul applications as well.
Microducts are empty tubes of small outer/inner diameter (e.g., generally in the range of 5/3.5 millimeters to 12/10 millimeters) that can be blown or pushed into empty or partially filled standard ducts. Microduct cables or microcables, specifically designed for this kind of application, are then installed as needed inside the microduct tubes by blown installation techniques.
There are various microduct cables on the market that are suited for different microduct inner diameter dimensions and holding a plurality of optical fibers inside.
U.S. Publication No. 2002/0061231 A1, for example, discloses a microcable including a metal or plastic tube of small diameter (preferably 3.5 to 5.5 mm) coated with a plastic layer (e.g., PTFE). The optical waveguides are then introduced into the tube either after the empty tube has been laid or at the factory.
U.S. Publication No. 2004/208463 A1 (and its European counterpart Publication No. EP 1,469,329) relate to a cable for use in air blowing installation. The cable includes at least one transmission medium of electrical or optical signals and a hollow cylindrical tube containing the transmission medium therein, the tube being formed at a surface thereof with a plurality of crater-shaped recesses.
Published U.K. Application No. GB 2,215,480 A relates to a cable element having a plurality of primary coated optical fibers laid in a juxtaposed configuration of a central fiber surrounded by the remaining fibers, the assembly being encapsulated in a plastic sheath.
U.S. Pat. No. 6,912,347 (and its European counterpart Publication No. EP 1,420,279) relate to a fiber optic cable with optical fibers stranded around a central strength member and surrounded by a thin outer jacket made of a low coefficient-of-friction material. The outer jacket is constructed to show the shape of the stranded optical fibers, thereby forming a textured outer surface.
U.S. Pat. No. 6,801,696 (and its European counterpart Publication No. EP 1,369,724) relate to an optical fiber cable structure including a tube having inorganic fillers dispersed within a soft resin. The tube houses optical fibers or ribbons surrounded by a water blocking material. The use of the inorganic fillers in the soft resin purportedly reduces the thermal expansion/contraction of the cable structure and increases the compression resistance of the cable structure to axial loads, providing protection to the optical fibers.
International Publication No. WO 2005/019894 relates to a cable that is suitable for push/pull installation in a microtube. The cable includes an outer sheath that surrounds at least one optical fiber. The outer sheath is made from a material blend of multiple thermoplastics having a modulus of elasticity of between about 1,000 and 2,500 MPa under normal use conditions, a thermal expansion coefficient of less than 1×104/° C., and a post-shrinkage coefficient of less than 0.1 percent.
U.S. Pat. No. 6,137,935 relates to an optical cable including at least one optical fiber surrounded by a tubular sheath, wherein a plastic inner layer and a plastic outer layer of the tubular sheath are extruded together around the optical fiber in a single operating step. Tension elements, which extend in the longitudinal direction of the optical cable, are embedded in the tubular sheath in the region between the inner layer and the outer layer.
U.S. Pat. No. 6,334,015 relates to a telecommunication cable having optical fibers contained in a retaining sheath, wherein the retaining sheath tightly grips a predetermined number (N) of optical fibers in a group (e.g., four, six, eight or twelve fibers), thereby constituting a compact module. A plurality of such optical fiber modules (i) can be combined within a protective jacket of a telecommunication cable or (ii) can be retained in a cylindrical sheath to form a bundle of several modules, with or without a central reinforcing member, which bundle is combined with other bundles of modules in a protective jacket of a telecommunication cable. Such a cable, however, is not regarded as a microcable.